The 33-year-old was immersed in a serious discussion in the nine black-and-white frames, assembled together as one portrait.

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Day will not go into detail about the afternoon or reveal what got the supermodel so animated at the three-hour photo-shoot at the model's north London home two months ago.

But some would be forgiven for thinking that in a couple of the snapshots, her subject looks a little worse for wear.

Moss, one of the most photographed women in the world, is wearing no make-up, although her eyelashes were curled for the commission.

A spokesman for the National Portrait Gallery in London, which is displaying the image in its permanent collection, said: "Forming one large work, each element of the portrait reveals a different expression, at times facing the camera head-on, at others in conversation or in quiet contemplation.

"Taken by Corinne Day in December 2006, the portrait brings something new to our perception of the enigma that is Kate Moss, among the most photographed women in the world today."

The model, in an on-off relationship with singer and drug addict Pete Doherty, looks alternatively angry, melancholic and pulls a face in the pictures.

British photographer Day was one of the first to work with Moss after she was discovered by Sarah Doukas at Storm at the age of 14.

Their infamous first collaboration in Vogue magazine in 1993 featured the waif-like model in what appeared to be a council flat in dreary underwear.

Day says of the new commission: "I suggested to Kate that we have a conversation about a serious subject. The subject she chose to talk about revealed her true feelings and in turn defined her character."

In a separate interview for the March issue of Vogue magazine, she adds: "I wanted the shots to be genuine, so that when people look at them, each picture will say something different.

"It's a cross-section of her personality - she was a little girl before and now she's a woman. Obviously there's life experience in her face, but she's still beautiful."

Moss said that she had not changed much since she first worked with Day.

"I've got crooked teeth, bow legs and a wonky nose," she says.

A former model and self-taught photographer, Day is renowned for bringing a hard-edged documentary look to fashion image-making.

She forms close relationships with many of her sitters, resulting in candid and intimate portraits.

The commission will go on display on February 12 and its unveiling coincides with the National Portrait Gallery's Face of Fashion exhibition on portraiture in fashion photography, which opens on February 15.

The exhibition features the work of acclaimed photographers such as Day, Mert Alas and Marcus Piggott, Steven Klein, Paolo Roversi and Mario Sorrenti.